The specific point in the cell cycle at which cell division stops is called a checkpoint or decision point. Cell cycle check points are:
1. G1/S Check Point: The cell cycle stops at the G1/S checkpoint when the cell is not suitable for division and the cell’s DNA is damaged. The cell cannot enter the S phase from the G1 phase. Here cell shape, cell hormones and DNA damage are checked.
2. G2/M Check Point: Cell cycle stops at G2/M checkpoint if damaged DNA of the cell is not repaired and DNA replication is not completed. The cell cannot enter the M phase from the G2 phase. Here the cell and nucleus size and DNA damage are checked.
3. M Check Point: Cell cycle stops at M Check Point when spindle fiber formation of cell is not complete and beam fiber is not properly attached to kinetochore. As a result, the process of mitosis does not occur.